Containers for beverages, and especially metal containers or cans for holding carbonated beverages, are produced in large quantities, exceeding 87 billion containers per year in the United States alone. This segment of the packaging industry is therefore very competitive, and manufacturers are constantly seeking ways to improve both the performance and economy of the product.
Most such containers are manufactured from aluminum, and are openable by a pull ring riveted on the end wall, which separates a tab from the end wall along a frangible score line, forming an opening through the end wall. Those containers manufactured and used in the United States generally push the tab into the opening, leaving it attached to the container. In some countries, however, most notably Japan, the tab is pulled outwardly away from the opening, and in many cases is separated from the container.
When the containers are used for carbonated beverages, they must be engineered with adequate strength to enable the pull tab to function properly, and to withstand internal pressures which may reach in excess of 95 pounds per square inch.
One of the areas of such containers which is particularly susceptible to these high internal pressures is the end wall, or lid, of the container. Unless the end wall is of sufficient thickness, and/or engineered with proper reinforcement, it may buckle or dome under pressure. This increases the risk that the pull tab will become snagged during handling in storage and shipment, causing a leak and destroying or damaging that as well as other, adjoining containers. Moreover, buckling of the end wall may also damage or destroy the seal between the container end wall and the side wall, resulting in the carbonation being lost from the contents of the container.
In spite of these difficulties, enormous savings could be realized by reducing the amount of material used in making the containers, and efforts have been made along those lines. The container side walls, for example, have been reduced in thickness to approximately 0.005 or 0.006 inches, and the container end walls are only approximately 0.0096 to 0.012 inches thick. These dimensions have been found to be about the practical lower limit for thickness, in order to still obtain satisfactory performance. In some cases, the diameter of the container end wall has been reduced slightly in order to save material.
While such measures may seem insignificant in the context of a single container, it should be kept in mind that substantial economy can be achieved when the amount of material saved in a single container is multiplied by the enormous number of containers that are manufactured.
Other efforts have been directed toward specific engineering features, such as reinforcing ribs, or special coining operations, in order to strengthen the container end wall, but it is generally believed that the practical limit has been reached with respect to reducing the amount of material used in the construction of such containers.
A simple and economical way of saving material in beverage containers, without sacrificing performance, would represent a substantial reduction in the cost of such containers, resulting in a significant competitive advantage in this segment of the packaging industry.